Cylindrical barrels have, for a considerable period of time, been a standard method of holding and moving merchandise in the industrial environment. Substantially all liquid and granular raw materials are provided and shipped in these barrels, to the extent that the standard oil drum, a steel barrel of some three foot height, capable of containing liquid contents of forty two gallons, has become a nearly universal size and shape standard for containers. As a result, such cylindrical drums usually made of steel or fiber material, have become a staple item of commerce. Because of their innate strength, low cost and volumetric efficiency, they have also become widely used for the holding and movement of intermediate products in the manufacturing industry, especially in the metal products field, where such drums are used as temporary holding containers for small and medium sized metal products, including castings, forgings, and products in the process of machining.
A typical liquid filled barrel or drum, such as the universally encountered oil drum, contains forty-two gallons of liquid, having a density slightly less than water; an alternate and almost as widely available drum is a fifty-five gallon barrel. Such drums come filled with products having densities in the range of six to eight pounds per gallon, and typically weigh between 300 to 500 pounds. Inasmuch as this is well beyond the strength which a single individual can safely lift, and approaches the maximum possible lifting load for two average men, numerous hand dolly and trucks have been devised for purpose of lifting and moving a single drum container.
All such hand trucks must accomplish several basic functions. The first is that the hand truck must somehow grasp and assist in tilting the barrel to a position where it is lifted from a floor for the purposes of moving. The truck must then hold the barrel so as to prevent its falling free during the course of movement, and the truck must somehow provide that a single average human manipulator can, exerting a reasonable amount of force, control and move the barrel and truck combination at whatever expected weight (mass) the total combination achieves.
The essential structure of a hand truck, old in the art, is of a vertical member against which the barrel is secured and rests, at least one pair of wheels so that the truck may be easily moved across uneven surfaces, and a handle for manipulating the same. In order to secure the barrel to the hand truck, it has become common to use any of a number of mechanisms for grasping the upper lip of the barrel and holding this in a fixed position against the frame of the truck. Thus, U.S. Pat. No. 1,513,863, to Sabin, shows an early form of barrel clasp having a fixed upper clasp which grips against the inner circumference of the rim of the barrel against the force of two spring loaded lifting members, which, activated by a short lever arm, are driven against the bottom edge of the out rim of the barrel; the combination holds the barrel against the vertical frame.
A later form of such a structure is shown in U.S. Pat. No. 2,447,300 to W. A. Williams, in which the bottom member is a fixed, partially circumferential edge and the outer lip of the barrel is held on to the top of this edge by a spring loaded outwardly acting hook member.
U.S. Pat. No. 1,510,456 discloses a structure in which an upper hook is looped over the rim of the barrel, and a pivoting lever arm on the hook forces a lower dog into lifting contact with the bottom surface of the outer rim of the barrel.
An inverted form of much the same structure is shown in U.S. Pat. No. 3,815,767 in which a spring loaded hook, the spring reacting through a lever arm, is engaged with the bottom surface of the outer rim of the barrel.
Double acting clasping hooks are shown in U.S. Pat. No. 2,616,577 to Barrett in which a cooperating spring loaded upper hook for grasping the inner edge of the rim of the barrel and a cooperating lower dog, also spring loaded, reacts against the bottom surface of the outer rim of the barrel. The entire comprises a self-contained structure which then may be vertically positioned along the frame of the lift truck for adapting to and clasping varying heights of barrels.
U.S. Pat. No. 2,272,447 discloses a second form of cooperating upper hook and lower lifting dog in which an eccentric offset on the pivot bearing for the upper hook is used to cause the upper hook to lower and then contract against the lifting dog to more securely fasten the barrel.
Most such devices use the lower dog or hook, set against the outer rim of the barrel, for the purposes of vertically restraining the barrel. All such trucks use the tilting motion of the lift truck, the barrel being so secured against the lift truck, to break the barrel free of the ground for movement. The great majority of current lift trucks pivot around a single provided front wheel pair, although Sabin discloses a truck frame in the form of a tricycle having a rear wheel which rests against the ground, limiting the rearward tilt of the truck.
Fiber drums, unlike steel drums, have no strong rim with a lip suitable for applying a lifting force. Two hand trucks, rather than using the lifting effect of a securing dog against the upper rim of the barrel, show the use of a hook to restrain the barrel against tilting away from the truck, and use a form of support or extension under the bottom edge of barrel to provide the lifting effect. These are U.S. Pat. No. 1,913,295 to Schreck and U.S. Pat. No. 2,485,085 to Burch. Burch also shows the use of an independent pivot axis, offset from the wheel axis for the truck. In Burch, the independent axis would cause the structure to fail to lift entirely were it not for the use of an intermediate stop or torsion spring and counter-balancing mechanism which converts the movement of the tilt frame to rotation about the wheel axis; thus, in order for the hand truck of Burch to physically lift the barrel from the ground, the lever arm of rotation is still about the wheel axis.
Schreck also discloses that of the class of hand trucks having a support under the barrel for lifting, the barrel must somehow be tilted forward in order to insert the support under the barrel.